Complementary metal oxide semiconductor image sensor and fabricating method thereof

ABSTRACT

A CMOS image sensor including a light-receiving element, at least one transistor, a first dielectric layer, a reflective layer, a second dielectric layer, a protective layer, a material layer, a transparent material layer, an optical filter, and a converging element is described. The light-receiving element and the transistor are disposed respectively inside the light sensing region and the transistor region. The first dielectric layer is disposed on the substrate, covering the transistor and the light-receiving element. The reflective layer is disposed on the first dielectric layer inside the light sensing region. The second dielectric layer is disposed on the first dielectric layer outside of the reflective layer. The material layer is disposed on the first dielectric layer inside of the reflective layer. The optical filter is disposed on the transparent material layer and the converging element is disposed on the optical filter inside the light sensing region.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention is related to an optical device and a fabricationmethod thereof. In particular, it is related to a CMOS image sensor anda fabrication method thereof.

2. Description of Related Art

Because CMOS image sensor (CIS) is compatible with CMOS technology, CIScan be easily integrated with other peripheral circuits on the samechip, thus greatly reducing the cost and consumption power of the imagesensor. Accordingly, during recent years, the importance of the CMOSimage sensor keeps increased and CIS has become dominant over chargecoupled device (CCD) in the lower-priced market applications.

U.S. Pat. No. 6,861,686 discloses a structure of a CMOS image sensor anda fabrication method thereof for resolving the issues derived from theuse of copper in replacement of aluminum for the fabrication ofinterconnect.

However, certain problems are still unsolved by U.S. Pat. No. 6,861,686.For instance, the external light passes through the lens, the colorfilter, into the metal interconnect line, and is then collected by thephotodiode. However, as the external light passes through the lightpassageway in the metal interconnect line, the external light may beabsorbed by the dielectric layer, protective layer, or other thin filmlayers on the surface of the light passageway if it does not directlyreach the photodiode. As a result, the photosensitivity of the CMOSimage sensor is reduced.

SUMMARY OF THE INVENTION

The objective for the present invention is to provide a complementarymetal-oxide semiconductor (CMOS) image sensor and a fabrication methodthereof, which is able to increase the light intensity sensed by theCMOS image sensor, thereby increasing the photosensitive efficiencythereof is increased.

The present invention proposes a CMOS image sensor, which includes alight-receiving element, at least one transistor, a first dielectriclayer, a reflective layer, a second dielectric layer, a protectivelayer, a material layer, a transparent material layer, an opticalfilter, and a converging element. The light-receiving element isdisposed inside the light sensing region in the substrate, thetransistor is disposed inside the transistor region in the substrate,and the transistor and the light-receiving element are electricallycoupled. Furthermore, the first dielectric layer is disposed on thesubstrate and the transistor and the light-receiving element are coveredby the first dielectric layer. In addition, the reflective layer isdisposed on the first dielectric layer inside the light sensing region.Furthermore, the second dielectric layer is disposed on the firstdielectric layer at an internal side of the reflective layer. Theprotective layer is disposed on the second dielectric layer, and thematerial layer is disposed on the first dielectric layer at an internalside of the reflective layer. The transparent material layer is disposedabove the material layer, the protective layer, and the reflectivelayer. The optical filter is disposed on the transparent material layer.The converging element is disposed on the optical filter inside thecorresponding light sensing region.

According to an embodiment of the present invention, the aforementionedreflective layer is, for example, a conductive layer. The material ofthe conductive layer is, for example, copper, aluminum, or tungsten.

According to an embodiment of the present invention, the aforementionedreflective layer is a conductive spacer structure. Furthermore, thereflective layer is formed from a plurality of conductive structurescoupling together.

According to an embodiment of the present invention, the CMOS imagesensor further includes an metal interconnect line which is disposedbetween the first dielectric layer and the second dielectric layerinside the transistor region. And the metal interconnect line and thetransistor are electrically coupled. The material of the reflectivelayer and the material of the metal interconnect line are the same. Inaddition, the aforementioned CMOS image sensor further includes a solderpad disposed in the protective layer and on a portion of the protectivelayer. And the solder pad and the metal interconnect line areelectrically coupled. The material of the reflective layer and thematerial of the solder pad are the same.

According to an embodiment of the present invention, the material of theaforementioned material layer and the material of the transparentmaterial layer are the same.

According to an embodiment of the present invention, the material of theaforementioned material layer is formed from the materials of the seconddielectric layer and of the protective layer.

According to an embodiment of the present invention, the aforementionedconverging element is, for example, a lens.

According to an embodiment of the present invention, the aforementionedlight-receiving element is, for example, a photodiode.

The present invention proposes a fabrication method of another CMOSimage sensor. First, a light-receiving element is formed inside thelight sensing region in the substrate. At least one transistorelectrically-coupled to the light-receiving element is formed at thetransistor region in the substrate. Later, the dielectric layer isformed on the substrate, wherein the metal interconnect line which iselectrically coupled to the transistor in the dielectric layer is formedinside the transistor region. Later, a protective layer is formed abovethe substrate, and the dielectric layer and the metal interconnect lineare covered by the protective layer. Later, a portion of the protectivelayer and a portion of the dielectric layer are removed, and a firstopening above the light-receiving element is formed. In addition, thereflective layer is formed on the sidewall of the first opening. Thetransparent material layer is then formed, and the protective layer andthe reflective layer are covered by the transparent material layer. Thefirst opening is filled. Later, the optical filter on the transparentmaterial layer is formed, and the converging element is formed on aportion of the optical filter inside the corresponding light sensingregion.

According to an embodiment of the present invention, the aforementionedreflective layer is, for example, a conductive layer. The material ofthe conductive layer is, for example, copper, aluminum, or tungsten.

According to an embodiment of the present invention, the fabricationmethod of the aforementioned reflective layer is, for example, first theformation of a conductive layer on the substrate, in which theprotective layer is covered by the conductive layer. The first openingis filled. Later, an anisotropic etching process is performed forremoving a portion of the conductive layer. A conductive spacerstructure is formed on the sidewall of the first opening for use as thereflective layer.

According to an embodiment of the present invention, the aforementionedreflective layer and the solder pad are formed at the same time. Thefabrication method is, for example, at the same time that the firstopening is formed, the formation of the second opening of the metalinterconnect line that is exposed on the second side of the protectivelayer inside the transistor region. Later, the conductive layer isformed above the substrate, and the protective layer is covered by theconductive layer. And the first opening and the second opening arefilled by the conductive layer. Later, a photoresist layer is formedabove a portion of the conductive layer corresponding to the secondopening. Later, an etching process is performed using the photoresistlayer as a mask for removing a portion of the conductive layer, forforming a solder pad in the second opening inside the transistor regionand on a portion of the protective layer at both sides, and for forminga reflective layer on the sidewall of the first opening of the lightsensing region at the same time.

According to an embodiment of the present invention, the fabricationmethod of the aforementioned metal interconnect line is, for example:(a) a first dielectric layer is formed at the first side, and atransistor and a light-receiving element are covered by the firstdielectric layer; (b) at least one plug for the electrically coupledtransistor is formed in the first dielectric layer; (c) at least oneconductor for the electrically coupled plug is formed above a portion ofthe first dielectric layer; (d) a second dielectric layer is formed onthe first dielectric layer of which is not yet covered by the conductor;and (e) step (a)-(d) are repeated for forming the predetermined layersof the metal interconnect lines.

According to an embodiment of the present invention, the fabricationmethod for the aforementioned metal interconnect line is, for example, adual damascene method.

According to an embodiment of the present invention, the aforementionedconverging element is, for example, a lens.

According to an embodiment of the present invention, the aforementionedlight-receiving element is, for example, a photodiode.

The present invention further proposes a fabrication method of a CMOSimage sensor. The light-receiving element is first formed in the lightsensing region in the substrate. At least one transistor for theelectrically coupled light-receiving element is formed inside thetransistor region in the substrate. Later, a first dielectric layer isformed on the substrate, wherein an metal interconnect line which iselectrically coupled to the transistor in the dielectric layer is formedinside the transistor region at the same time. At least one firstconductive structure which is not coupled to the light-receiving elementis formed in a portion of the dielectric layer inside the light sensingregion. Later, a protective layer is formed above the substrate, and thedielectric layer, the conductive structure, and the metal interconnectline are covered by the protective layer. A transparent material layeris formed on the protective layer. Furthermore, an optical filter isformed on the transparent material layer, and a converging element isformed on a portion of the optical filter inside the corresponding lightsensing region.

According to an embodiment of the present invention, the material of theaforementioned first reflective layer is, for example, a conductivelayer. The material of the conductive layer is, for example, copper,aluminum, or tungsten.

According to an embodiment of the present invention, the aforementionedfirst conductive structure and the metal interconnect line are formed atthe same time, wherein the fabrication method is, for example: (a) afirst dielectric layer is formed on the substrate; (b) a plug for thetransistor which is electrically coupled inside the first dielectriclayer is formed; (c) a conductor which is electrically coupled to theplug is formed above the first dielectric layer inside the transistorregion, and at the same time a conductive structure is formed above thefirst dielectric layer inside the light sensing region; (d) a seconddielectric layer is formed on the first dielectric layer which is notcovered by the conductor and the conductive structure; and (e) step(a)-(d) are repeated for forming the predetermined layers of the metalinterconnect lines. The fabrication method of the metal interconnectline is, for example, the dual damascene fabrication method.

According to an embodiment of the present invention, a second reflectivelayer is further formed in the protective layer inside the light sensingregion, and the second reflective layer is correspondingly formed on thefirst reflective layer. The fabrication method for the second reflectivelayer is, for example, the forming of an opening or a trench on theprotective layer inside the light sensing region. Later, a conductivelayer is formed above the substrate, and the protective layer is coveredby the conductive layer, and the opening or the trench is filled. Later,an etching process is performed for removing a portion of the conductivelayer and for forming a second reflective layer in the sidewall of theopening or trench. Furthermore, the second reflective layer and a solderpad are formed at the same time, wherein the fabrication method is, forexample, the forming of the first opening of the first reflective layerexposed at the first side in the protective layer inside the lightsensing region, and the forming of the second opening of the metalinterconnect line exposed at the first side in the protective layerinside the transistor region. Later, a conductive layer is formed on thesubstrate, and the protective layer is covered by the conductive layer.The first opening and the second opening are filled by the conductivelayer. Later, a photoresist layer is formed at above a portion of theconductive layer corresponding to the second opening. Later, an etchingprocess is performed using a photoresist layer as a mask for removing aportion of the material layer. A solder pad is formed in the secondopening of the transistor region and on a portion of the protectivelayer at both sides, and at the same time the second reflective layer isformed in the protective layer inside the light sensing region.

According to an embodiment of the present invention, the aforementionedconverging element is, for example, a lens.

According to an embodiment of the present invention, the aforementionedlight-receiving element is, for example, a photodiode.

A reflective layer is fabricated in the present invention inside theimage sensor for reflecting the light to increase the light intensitysensed by the image sensor and to improve the photosensitive efficiencyof the image sensor. In addition, the reflective layer can be formed atthe same time as the solder pad; therefore, the process is simple andfabrication cost can be saved. Furthermore, the reflective layer can beformed at the same time as the metal layer of the interconnect layer,which can likewise save fabrication cost.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a cross-sectional view schematically illustrating a CMOS imagesensor, according to an embodiment of the present invention.

FIG. 2A to FIG. 2G are cross-sectional views schematically illustratinga fabrication process for the CMOS image sensor, according to anembodiment of the present invention.

FIG. 3 is a cross-sectional view schematically illustrating aninterconnect layer for the CMOS image sensor, according to an embodimentof the present invention.

FIG. 4A to FIG. 4C are cross-sectional views schematically illustratingthe fabrication process for the CMOS image sensor, according to anotherembodiment of the present invention.

FIG. 5 is a cross-sectional view schematically illustrating aninterconnect layer for the CMOS image sensor, according to anotherembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a cross-sectional view schematically illustrating a CMOS imagesensor, according to an embodiment of the present invention.

Referring to FIG. 1, the CMOS image sensor of the present inventionincludes a light-receiving element 102, a transistor 104, a reflectivelayer 142, a protective layer 136, a transparent material layer 146, amaterial layer 145, an optical filter 148, a converging element 150, anda dielectric layer 106, 107. The light-receiving element 102 is disposedinside the light sensing region 101 of the substrate 100. Thelight-receiving element 102 is, for example, a photodiode. Thetransistor 104 is disposed inside the transistor region 103 of thesubstrate 100, and the transistor 104 and the light-receiving element102 are electrically coupled. The transistor 104 includes a gatedielectric layer 104 a, a gate 104 b, a source/drain region 104 c and aspacer 104 d. The dielectric layer 106 is disposed on the substrate 100,and the transistor 104 and the light-receiving element 102 are coveredby the dielectric layer 106. The reflective layer 142 is disposed on thedielectric layer 106 inside the light sensing region 101. The reflectivelayer 142 is, for example, a conductive layer. The material of theconductive layer is, for example, copper, aluminum, tungsten or otherappropriate conductive materials. In particular, the reflective layer142 is, for example, a tubular conductive spacer structure, or it isformed from a plurality of tubular conductive structures couplingtogether. Furthermore, the dielectric layer 107 is disposed on thedielectric layer 106 outside of the tubular reflective layer 142. Andthe protective layer 136 is disposed on the dielectric layer 107. Thematerial for the protective layer 136 is, for example, silicon oxide,silicon carbide, silicon nitride, or other appropriate materials.Furthermore, the material layer 145 is disposed on the dielectric layer106 and inside of the reflective layer 142. The transparent materiallayer 146 is disposed on top of the material layer 145 and thereflective layer 142, and on the protective layer 136. The material ofthe transparent material layer 146 can be, for example, dielectricmaterials, i.e. silicon oxide or silicon nitride, or photoresistmaterials. In an embodiment of the present invention, the material ofthe material layer 145 and the material of the transparent materiallayer 146 are the same. In another embodiment of the present invention,the material layer 145 is formed from two materials, the same materialsof the dielectric layer 107 and the protective layer 136. Furthermore,the optical filter 148 is disposed on the transparent material layer146, and the converging element 150 is disposed on the optical filter148 inside the range of the light sensing region 101. The convergingelement 150 is, for example, a lens.

In an embodiment of the present invention, the CMOS image sensor furtherincludes an metal interconnect line 134 disposed between the dielectriclayers 106, 107 for coupling the transistor 104. Furthermore, thematerial of the reflective layer 142 can be the same as tha of the metalinterconnect line 134.

In another embodiment of the present invention, the CMOS image sensorfurther includes a solder pad 144 disposed in the protective layer 136and extended to the transparent material layer 146 on the protectivelayer 136. The solder pad 144 and the metal interconnect line 134 areelectrically coupled. Furthermore, the material of the reflective layer142 is the same as the material of the solder pad 144.

Indeed, the metal interconnect line 134 having three layers ofinterconnect layers is used as an illustrative example in theaforementioned embodiment. However, the metal interconnect line in thepresent invention is not limited by the examples. The number of layersof the metal interconnect line 134 can be modified based on the circuitdesign or process requirements.

Importantly, as illustrated in a light path 152 in FIG. 1, when lightenters into the CMOS image sensor, the converging element 150 is able tofocus light, so that light passes through the optical filter 148,penetrates the transparent material layer 146, the material layer 145,and the dielectric layer 106, and then is collected by thelight-receiving element 102 disposed in the substrate 100. On the otherhand, if light focused by the converging element 150 passes through theoptical filter 148 and is not directly impacted on the light-receivingelement 102, the reflective layer 142 is able to reflect and redirectlight to the light-receiving element 102 as shown in the light path 154.

In other words, the reflective layer 142 is able to reflect the light tothe light-receiving element 102, thus increasing the light detectionintensity by the CMOS image sensor and enhancing the photosensitivitythereof. As a result, the conventional issues of light absorbance by thedielectric layer and other thin films can be resolved, and thephotosensitive efficiency of the image sensor is thereby improved. Mostimportantly, as the size of the light-receiving element 102 decreaseswith higher integration of the device, the detected light intensity isalso decreased. However, the reflective layer 142 is capable ofimproving photosensitive efficiency of the CMOS image sensor.

Furthermore, the fabrication method for the CMOS image sensor isillustrated by means of two embodiments in the present invention, butthe present invention is not limited hereto. One of the major featuresis that a reflective layer is formed inside the CMOS image sensor forreflecting the incident light.

FIG. 2A to FIG. 2G are cross-sectional views schematically illustratinga fabrication process for the CMOS image sensor, according to anembodiment of the present invention, wherein in FIG. 2A to FIG. 2G, thecomponents that are the same as in FIG. 1 have the same referencenumbers.

Referring to FIG. 2A, the light-receiving element 102 is formed insidethe light sensing region 101 in the substrate 100. At least onetransistor 104 is formed inside the transistor region 103 on thesubstrate 100, and the transistor 104 and the light-receiving element102 are electrically coupled. The light-receiving element 102 is, forexample, a p-n junction photodiode in the substrate 100. In other words,the light-receiving element 102 is, for example, formed by forming ann-doped region in a p-type substrate. Furthermore, the aforementionedtransistor 104 includes the gate dielectric layer 104 a, the gate 104 b,the source/drain region 104 c and the spacer 104 d.

Later, referring to FIG. 2B, the metal interconnect line 134 which iscoupled to the transistor 104 is formed on the substrate 100. Theexemplary fabrication method is described as follows. At first, adielectric layer 106 is formed on the substrate 100. Later, a plug 110is formed in the dielectric layer 106. The conductor 116 which iselectrically coupled to the plug 110 is formed above the dielectriclayer 106. The dielectric layer 112 is formed on the dielectric layer106 which is not covered by the conductor 116. Later, the dielectriclayer 118, the plug 120, the conductor 124, the dielectric layer 122,the dielectric layer 126, the plug 128, the conductor 132, and thedielectric layer 130 are formed sequentially and independently byrepeating the above processes. The material of the aforementioned plugs110, 120, 128 and the conductors 116, 124, 132 can be, for example,copper, aluminum, tungsten, or other appropriate metals.

In an embodiment of the present invention, the metal interconnect line134, for example, is able to use the dual damascene technology forforming the plug and the conductor at the same time. Referring to FIG.3, the dielectric layer 106 and the dielectric layer 112 are firstsequentially formed. The trench 114 is later formed in the dielectriclayer 112 inside the transistor region 103. An opening 108 is formed inthe dielectric layer 106 and the metal layer is filled into the opening108 to form the damascene structure 115. Later, the aforementionedprocedures are repeated, so that the dielectric layer 118, thedielectric layer 122, the damascene structure 123, the dielectric layer126, the dielectric layer 130, and the damascene structure 131 aresequentially formed to complete the metal interconnect line 134.

Referring to FIG. 2C, a protective layer 136 is formed above thesubstrate 100. The material for the protective layer 136 is, forexample, silicon oxide, silicon carbide, silicon nitride, or otherappropriate materials, formed by chemical vapor deposition or otherappropriate methods. The function of the aforementioned protective layer136 is for protecting the metal layer 132 in the interconnect layer 134from damages.

Later, referring to FIG. 2D, a portion of the protective layer 136 and aportion of the interconnect layer 134 are removed to form an opening 138above the light-receiving element 102. The fabrication of the opening138, for example, includes forming a patterned photoresist layer (notshown) on the protective layer 136, and etching a portion of theprotective layer 136 and a portion of the interconnect layer 134 byusing the patterned photoresist layer as a mask.

Referring to FIG. 2E, a reflective layer 142 is formed on the sidewallof the opening 138. The material of the reflective layer 142 is, forexample, copper, aluminum, tungsten, or other appropriate conductivematerial. In addition, the fabrication for the reflective layer 142, forexample, includes forming a conductive layer (not shown) above thesubstrate 100 and in the opening 138, and performing an anisotropicetching process for removing a portion of the conductive layer, so as toform a tubular conductive spacer structure surrounded by the sidewall ofthe opening 138, which refers as the reflective layer 142.

In an embodiment of the present invention, the conductive layer 142 isformed at the same time as the solder pad 144; therefore, the process isrelatively simple, and fabrication cost is lower. The fabrication of thesolder pad 144, for example, includes forming the solder pad opening 140in the protective layer 136 to expose the metal layer 132at the sametime as the opening 138 is formed. Later, a conductive layer (not shown)is formed above the substrate 100, covering the protective layer 136 andfilling the openings 138, 140. Later, a photoresist layer (not shown) isformed on the conductive layer at the location corresponding to thesolder pad opening 140. Later, an etching process is performed by usingthe photoresist layer as a mask, a portion of the conductive layer isremoved to form a solder pad 144 (as shown in FIG. 2E) in the opening140 and on the protective layer 136 at both sides of the opening 140 andto form the reflective layer 142 on the sidewall of the opening 138 atthe same time. Afterwards, the photoresist layer is removed. In thepresent embodiment, the reflective layer 142 and the solder pad 144 areformed of the same material. Furthermore, the aforementioned solder pad144 is electrically coupled to the metal interconnect line 134, and usedas external access for the device on the substrate 100.

Later, referring to FIG. 2F, a transparent material layer 146 is formedabove the substrate 100. The solder pad 144, the protective layer 136and the conductive layer 142 are covered by the transparent materiallayer 146. In addition, the opening 138 is filled by the transparentmaterial layer 146. The material of the transparent material layer 146is, for example, silicon oxide, silicon nitride, other dielectricmaterials, or photoresist materials.

Later, referring to FIG. 2G, an optical filter 148 is formed on thetransparent material layer 146. The optical filter 148, for example, isa color filter for allowing certain designated wavelength of light forpassing through. The optical filter 148 typically has three differentcolors (i.e. red, blue, and green). Later, a converging element 150 isformed on a portion of the optical filter 148 inside the correspondinglight sensing region 101. The converging element 150 is, for example, alens.

FIG. 4A to FIG. 4C are cross-sectional views schematically illustratingthe process of fabricating the CMOS image sensor, according to anotherembodiment of the present invention. In FIG. 4A to FIG. 4C, thecomponents which are the same as in FIG. 1 and having the same referencenumbers are ignored.

First, referring to FIG. 4A, the light-receiving element 102 is formedinside the light sensing region 101 in the substrate 100. At least onetransistor 104 is formed inside the transistor region 103 in thesubstrate 100, The transistor 104 and the light-receiving element 102are electrically coupled.

Referring to FIG. 4B, a metal interconnect line 134 is formed inside thetransistor region 103, and at the same time a reflective layer 137 isformed inside the light sensing region 101. The metal interconnect line134 can be formed by firstly forming the dielectric layer 106 above thesubstrate 100 and then forming the plug 110 within the dielectric layer106. Later, a metal layer (not shown) is deposited on the dielectriclayer 106 and then patterned in order to form a conductor 116 inside thetransistor region 103 and a conductive structure 117 inside the lightsensing region 101 at the same time. Later, the dielectric layer 118,the plug 120, the conductive structure 121, the conductor 124, theconductive structure 125, the dielectric layer 122, the dielectric layer126, the plug 128, the conductive structure 129, the conductor 132, theconductive structure 133, and the dielectric layer 130 are sequentiallyformed according to the aforementioned processes. The aforementionedconductive structures 117, 121, 125, 129, 133 form the reflective layer137. For example, the aforementioned conductive structures arering-like, and thus form a tubular reflective layer. The material forthe plugs 110, 120, 128 and the conductors 116, 124, 132 can be, forexample, copper, aluminum, tungsten, or other appropriate metal. And thematerial for the reflective layer 137, the plugs 110, 120, 128, and theconductors 116, 124, 132 are the same. In particular, because thereflective layer 137 can be formed at the same time as the metalinterconnect line 134 is formed, the fabrication process is simplifiedand more cost-effective.

In an embodiment of the present invention, the plugs and the conductorsin conventional interconnect can be formed using the dual damascenetechnology for the metal interconnect line 134. Similarly, when formingthe metal interconnect line 134, the reflective layer 137 is formed atthe same time. Referring to FIG. 5, the fabrication method includesfirstly forming the dielectric layer 106 and the dielectric layer 112sequentially. Later, the trench 114 is formed in the dielectric layer106 and the dielectric layer 112 inside the transistor region 103. Theopening 108 is formed in the dielectric layer 106 and at the same timethe trench 151 is formed in the dielectric layer 106 and the dielectriclayer 112 inside the light sensing region 101. After filling a metalmaterial layer into the trench 151, the damascene structure 115 isformed within the transistor region 103 and the conductive structure 152is formed within the light sensing region 101. The aforementioned stepsare repeated and the dielectric layer 116, the dielectric layer 122, thedamascene structure 123, the conductive structure 154, the dielectriclayer 126, the dielectric layer 130, the damascene structure 131, andthe conductive structure 156 are sequentially formed to complete thefabrication of the metal interconnect line 134 and the reflective layer137.

Referring to FIG. 4C, the protective layer 136 is formed above thesubstrate 100. Later, the transparent material layer 146 is formed onthe protective layer 136 and the optical filter 148 is formed on thetransparent material layer 146. In addition, the converging element 150is formed on a portion of the optical filter 148 inside thecorresponding light sensing region 101.

In another embodiment of the present invention, after forming theprotective layer 136, a reflective layer 135 can further be formed inthe protective layer 136 inside the light sensing region 101. Thereflective layer 135 is formed right on the reflective layer 137. Thereflective layer 135 can be formed by, for example, forming an openingor a ring-like trench in the protective layer 136 to expose thereflective layer 133 and a conductive layer (not shown) is formed overthe protective layer 136. Later, an etching process is performed forremoving the extra conductive layer so as to form the reflective layer135 either on the sidewall of the opening or within the ring-liketrench. If the reflective layer 135 is formed on the sidewall of theopening in the protective layer 136, the transparent material layer 146,which is pre-fabricated, is formed covering the protective layer 136 andthe reflective layer 135 and filled the opening. That is, the reflectivelayer 135 and the transparent material layer 146 are made of the samematerial. Furthermore, if the reflective layer 135 is formed within thering-like trench in the protective layer 136, a portion of theprotective layer 136 is disposed inside the reflective layer 135.

Furthermore, the reflective layer 135 and the solder pad 144 can beformed at the same time. For example, during forming the opening or thetrench in the protective layer 136 to expose the reflective layer 133,the solder pad opening 140 is formed in the protective layer 136 at thesame time to expose the metal layer 130. Later, a conductive layer (notshown) is formed above the substrate 100 covering the protective layer136. After forming a photoresist layer ( not shown), an etching processis performed using the photoresist layer as a mask for removing aportion of the conductive layer, thus forming the solder pad 144 on theprotective layer 136 within the transistor region 103 and forming thereflective layer 135 inside the light sensing region 101 at the sametime. Later, the photoresist layer is removed.

In summary, the present invention includes the following advantages.

1. The present invention provides a tubular reflective layer above thelight-receiving element or photodiode, and the reflective layer iscapable of reflecting light to the light-receiving element or photodiodefor increasing the detected light intensity by the light-receivingelement or photodiode, thereby increasing the photosensitive efficiencyof the image sensor.

2. The reflective layer of the present invention can be formedsimultaneously with the solder pad; therefore, the fabrication processis simplified, and the fabrication costs become lower.

3. The reflective layer in the present invention can be formedsimultaneously with the metal layer(s) inside the interconnect metallayer.

4. The present invention can improve the photosensitive efficiency forthe image sensor by increasing the light intensity detected by thelight-receiving element or the photodiode.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing descriptions, it is intended that the presentinvention covers modifications and variations of this invention if theyfall within the scope of the following claims and their equivalents.

1. A complementary metal-oxide semiconductor (CMOS) image sensor,comprising: a light-receiving element, disposed in a light sensingregion of a substrate; at least one transistor, disposed inside atransistor region of the substrate, and the transistor and thelight-receiving element are electrically coupled; a first dielectriclayer, disposed on the substrate covering the transistor and thelight-receiving element; a reflective layer, disposed on the firstdielectric layer inside the light sensing region; a second dielectriclayer, disposed on the first dielectric layer outside of the reflectivelayer; a protective layer, disposed on the second dielectric layer; amaterial layer, disposed inside of the reflective layer on the firstdielectric layer; a transparent material layer, disposed above thematerial layer, the protective layer, and the reflective layer; anoptical filter, disposed on the transparent material layer; and aconverging element, disposed on the optical filter inside the lightsensing region.
 2. The CMOS image sensor according to claim 1, whereinthe reflective layer comprises a conductive layer.
 3. The CMOS imagesensor according to claim 2, wherein a material of the conductive layercomprises copper, aluminum, or tungsten.
 4. The CMOS image sensoraccording to claim 1, wherein the reflective layer is a conductivespacer structure.
 5. The CMOS image sensor according to claim 1, whereinthe reflective layer is formed of a plurality of conductive structurescoupling together.
 6. The CMOS image sensor according to claim 1,further comprising a metal interconnect line, disposed in the firstdielectric layer and the second dielectric layer within the transistorregion, and electrically coupled to the transistor.
 7. The CMOS imagesensor according to claim 6, wherein a material of the reflective layerand a material of the metal interconnect line are the same.
 8. The CMOSimage sensor according to claim 6, further comprising a solder pad,disposed in the protective layer and within the transparent materiallayer on the protective layer, and electrically coupled to the metalinterconnect line.
 9. The CMOS image sensor according to claim 8,wherein a material of the reflective layer and a material of the solderpad are the same.
 10. The CMOS image sensor according to claim 1,wherein a material of the material layer and a material of thetransparent material layer are the same.
 11. The CMOS image sensoraccording to claim 1, wherein the material layer is comprised of amaterial of the second dielectric layer and a material of the protectivelayer.
 12. The CMOS image sensor according to claim 1, wherein theconverging element comprises a lens.
 13. The CMOS image sensor accordingto claim 1, wherein the light-receiving element comprises a photodiode.14. A fabrication method of a CMOS image sensor, comprising: forming alight-receiving element inside a light sensing region in a substrate;forming at least one transistor which is electrically coupled to thelight-receiving element inside the transistor region on the substrate;forming a dielectric layer on the substrate, wherein a metalinterconnect line electrically coupled to the transistor is formed inthe dielectric layer inside the transistor region; forming a protectivelayer above the substrate, covering the dielectric layer and the metalinterconnect line; removing a portion of the protective layer and aportion of the dielectric layer to form a first opening above thelight-receiving element; forming a reflective layer on a sidewall of thefirst opening; forming a transparent material layer, covering theprotective layer and the reflective layer and filling the first opening;forming an optical filter on the transparent material layer; and forminga converging element on a portion of the optical filter inside the lightsensing region.
 15. The fabrication method of a CMOS image sensoraccording to claim 14, wherein the reflective layer comprises aconductive layer.
 16. The fabrication method of a CMOS image sensoraccording to claim 15, wherein a material of the conductive layercomprises copper, aluminum, or tungsten.
 17. The fabrication method of aCMOS image sensor according to claim 14, wherein the step of forming thereflective layer further comprises: forming a conductive layer above thesubstrate, covering the protective layer, and filling the first opening;and performing an anisotropic etching process, removing a portion of theconductive layer to form a conductive spacer structure on the sidewallof the first opening as the reflective layer.
 18. The fabrication methodfor an image sensor according to claim 14, wherein the reflective layerand a solder pad are formed at the same time.
 19. The fabrication methodfor a CMOS image sensor according to claim 18, wherein the step offorming the solder pad further comprises: forming a second openingexposing the metal interconnect line in the protective layer within thetransistor region at the same time as the first opening within the lightsensing region is formed; forming a conductive material layer above thesubstrate, covering the protective layer and filling the first openingand the second opening; forming a photoresist layer above the conductivematerial layer corresponding to the second opening; performing anetching process, using the photoresist layer as mask, to remove aportion of the conductive material layer, so that a solder pad in thesecond opening and on the protective layer at both sides of the openingis formed inside the transistor region and the reflective layer on thesidewall of the first opening inside the light sensing region is formedat the same time; and removing the photoresist layer.
 20. Thefabrication method of a CMOS image sensor according to claim 14, whereinthe converging element comprises a lens.
 21. The fabrication method of aCMOS image sensor according to claim 14, wherein the light-receivingelement comprises a photodiode.
 22. A fabrication method of a CMOS imagesensor, comprising: forming a light-receiving element in a light sensingregion in a substrate; forming at least one transistor which iselectrically coupled to the light-receiving element inside a transistorregion in the substrate; forming a dielectric layer on the substrate,wherein a metal interconnect line electrically coupled with thetransistor is formed in the dielectric layer inside the transistorregion, and simultaneously at least one first conductive structure isformed in the dielectric layer inside the light sensing region withoutcoupling with the light-receiving element; forming a protective layerabove the substrate, covering the dielectric layer, the conductivestructure and the metal interconnect line; forming a transparentmaterial layer on the protective layer; forming an optical filter on thetransparent material layer; and forming a converging element on aportion of the optical filter corresponding to the light sensing region.23. The fabrication method for a CMOS image sensor according to claim22, wherein a material for the first reflective layer comprises aconductive layer.
 24. The fabrication method for a CMOS image sensoraccording to claim 23, wherein a material for the conductive layercomprises copper, aluminum, or tungsten.
 25. The fabrication method fora CMOS image sensor according to claim 22, wherein the step for formingthe first conductive structure and the metal interconnect linecomprises: (a) forming a first dielectric layer on the substrate; (b)forming a plug which is electrically coupled to the transistor insidethe first dielectric layer; (c) forming a conductor which iselectrically coupled to the plug on the first dielectric layer in thetransistor region, and at the same time forming a conductive structureabove the first dielectric layer inside the light sensing region; (d)forming a second dielectric layer on the first dielectric layer which isnot covered by the conductor and the conductive structure; and (e)repeating steps (a)-(d), for forming predetermined layers of the metalinterconnect line.
 26. The fabrication method of a CMOS image sensoraccording to claim 25, wherein the step for forming the metalinterconnect line further comprises: (a) forming the first dielectriclayer and a second dielectric layer sequentially above the substrate;(b) forming a first trench in the second dielectric layer inside thetransistor region and forming a first opening which is coupled to thefirst trench in the first dielectric layer, and simultaneously forming afirst ring trench in the second dielectric layer inside the lightsensing region; (c) filling a first conductive layer into the firsttrench, the first opening and the first ring trench to form a firstdamascene structure in the first dielectric layer and the seconddielectric layer inside the transistor region, and to form a firstconductive structure in the second dielectric layer inside the lightsensing region; (d) forming a third dielectric layer and a fourthdielectric layer above the second dielectric layer sequentially; (e)forming a second trench in the fourth dielectric layer inside thetransistor region, forming a second opening which is coupled with thesecond trench in the third dielectric layer, and simultaneously forminga second ring trench in the fourth dielectric layer and the thirddielectric layer inside the light sensing region; (f) filling a secondconductive layer into the second opening, the second trench and thesecond ring trench to form a dual damascene structure in the fourthdielectric layer and the third dielectric layer inside the transistorregion and form a second conductive structure in the fourth dielectriclayer and the third dielectric layer inside the light sensing region;and (g) repeating steps (d)-(f) for forming predetermined layers of themetal interconnect line.
 27. The fabrication method of a CMOS imagesensor according to claim 22, further comprising forming a secondreflective layer in the protective layer inside the light sensingregion, and the second reflective layer is formed correspondingly to thefirst reflective layer.
 28. The fabrication method of a CMOS imagesensor according to claim 27, wherein step of forming the secondreflective layer comprises: forming a third opening or a third ringtrench in the protective layer inside the light sensing region; forminga third conductive layer above the substrate, covering the protectivelayer and filling the third opening or the third ring trench; andperforming an etching process to remove a portion of the thirdconductive layer, so that the second reflective layer is formed on asidewall of the third opening or the third ring trench.
 29. Thefabrication method of a CMOS image sensor according to claim 27, whereinthe second reflective layer and a solder pad are formed at the sametime.
 30. The fabrication method of a CMOS image sensor according toclaim 29, wherein the step of forming the solder pad comprises: formingthe third opening or the third ring trench exposing the first reflectivelayer and in the protective layer inside the light sensing region, andforming a fourth opening exposing the metal interconnect line and in theprotective layer inside the transistor region; forming the thirdconductive layer above the substrate, covering the protective layer andfilling the third opening and the fourth opening; forming a photoresistlayer above a portion of the third conductive layer corresponding to thefourth opening; performing an etching process, using the photoresistlayer as mask, to remove a portion of the third conductive layer, inorder to form the solder pad in the fourth opening and in the protectivelayer inside the transistor region, and to form the second reflectivelayer at the same time inside the light sensing region; and removing thephotoresist layer.
 31. The fabrication method of a CMOS image sensoraccording to claim 22, wherein the converging element comprises a lens.32. The fabrication method of a CMOS image sensor according to claim 22,wherein the light-receiving element comprises a photodiode.